This invention relates to a puffer type gas circuit breaker.
A prior-art, puffer type gas circuit breaker has been constructed as shown in FIGS. 1a and 1b. FIG. 1a illustrates the closed contact state of the prior-art, puffer type bidirectional-gas-blast circuit breaker, while FIG. 1b illustrates the open contact state of the circuit breaker.
Referring to the figures, numeral 1 designates a terminal plate on a power supply side, and numeral 2 a terminal plate on a load side. Numeral 3 designates a current-carrying stationary contact on the power supply side, which is attached at one end thereof to the terminal plate 1, the other end of which is constructed by annularly arraying a plurality of finger contacts, and which is brought into sliding contact with or disengage from a puffer cylinder 4 to be described below. The puffer cylinder 4 also serves as a current-carrying movable contact, and moves in relation to a rod 6 to be described below. Shown at numeral 5 is a current-carrying stationary contact on the load side, which is attached at one end thereof to the terminal plate 2, the other end of which has a plurality of finger contacts arrayed annularly, and which is brought into sliding contact with or disengaged from the puffer cylinder 4. The rod 6 is driven in the axial direction thereof by a driving mechanism, not shown, through an insulating rod, not shown. The rod 6 is formed at one end thereof with an opening 61 and at the other end thereof with communicating holes 62 which are formed perpendicular to the axial direction thereof, as well as being fixed at said one end to a supporter 7. A finger-shaped movable arc contact 8 is also fixed to the supporter 7. A cylindrical stationary arc contact 9 which can be brought into and out of contact with the movable arc contact 8, has gas holes 91 and 92 formed at both of its ends, and is fixed at one end thereof to the terminal plate 1. The terminal plate 1 is formed with a gas hole 100, which communicates with the gas hole 91 of the stationary arc contact 9.
Shown at numeral 10 is a puffer piston. A puffer chamber 11 is defined by the puffer piston 10, the puffer cylinder 4, the supporter 7 and the rod 6. Numeral 12 indicates a fluid guide which is made of an insulating material such as teflon, which is arranged coaxially and concentrically with the stationary arc contact 9, and which is fixed to the rod 6 through the supporter 7. Numeral 13 indicates a fluid guide which is also made of an insulating material such as teflon, which is arranged coaxially and concentrically with the stationary arc contact 9, and which is fixed to the rod 6 in a manner to surround the movable arc contact 8. Both the fluid guides 12 and 13 are respectively formed with openings 121 and 131 so that the stationary arc contact 9 can be snugly inserted therethrough. The supporter 7 has communicating holes 71 formed therein. As will be described later, an arc extinguishing fluid (for example, SF.sub.6 gas) contained in the puffer chamber 11 passes through the communicating holes 71 at a low temperature and becomes a high speed, high pressure gas stream approaching the speed of sound and circulates through a passage 14 defined by both the fluid guides 12 and 13, whereupon the fluid is forcibly blown against an electric arc 15 via a nozzle 141, 131 formed in the fluid guides 12 and 13, respectively.
The operations of then prior art gas circuit breaker will be explained hereinafter.
Under the closed contact state shown in FIG. 1a , current flows from the power supply side terminal plate 1 to the load side terminal plate 2 via the stationary contact 3, puffer cylinder (movable contact) 4 and stationary contact 5 in the order mentioned. In addition, part of the current flows from the power supply side terminal plate 1 to the load side terminal plate 2 via the stationary arc contact 9, movable arc contact 8, supporter 7, puffer cylinder (movable contact) 4 and stationary contact 5 in the order mentioned.
Next, when the contacts are opened, as illustrated in FIG. 1b , the rod 6 is caused to descend by an insulating rod connected therewith, not shown, which is connected to a driving mechanism, not shown. With the downward movement of the rod 6, the puffer cylinder 4 simultaneously moves downward, so that the arc extinguishing fluid in the puffer chamber 11 is forcibly compressed. The arc extinguishing fluid at the low temperature compressed forcibly flows into the passage 14 via the communicating holes 71 as indicated by arrows a. Part of the arc extinguishing fluid is discharged into a container (not shown), filled with the fluid, along a path indicated by arrows b, c, d, e and f by passing through the opening 131 of the fluid guide 13, the opening 61 of the rod 6, the interior of the rod 6 and the communicating holes 62 of the rod 6 in the order mentioned. Another part of the arc extinguishing fluid is discharged through the gas hole 92 of the stationary arc contact 9 into the container (not shown) along a path indicated by arrows g, h, i and j by passing through the interior and gas hole 91 of the stationary arc contact 9 and the gas hole 100 of the terminal plate 1. Further, another part is discharged from the opening 121 of the fluid guide 12 into the container (not shown) as indicated by an arrow k.
The electrical interrupting operation will be generally explained hereinafter.
When the rod 6 descends, the puffer cylinder or movable contact 4 is first disengaged from the stationary contact 3. The movable arc contact 8 is subsequently disengaged from the stationary arc contact 9, so that the electric arc 15 develops between the movable arc contact 8 and the stationary arc contact 9. The arc 15 is extended downward with the descent of the movable arc contact 8, while at the same time the low temperature gas stream from the puffer chamber 11 is forcibly blown against the arc 15 at a velocity approaching the speed of sound. Thus, the foot 151 of the arc 15 on the power supply side is forcibly moved toward the terminal plate 1, and the foot 152 on the load side is forcibly moved toward the terminal plate 2. In addition, the arc 15 is bilaterally extended within the stationary arc contact 9 at one end thereof and within the movable arc contact 8 and rod 6 at the other end thereof. In this way, the arc 15 is lengthened to increase its resistance, so that the arc current is limited. Further, the arc is exposed to the low temperature arc extinguishing fluid travelling at a high speed and having a high insulating property. Consequently, the thermal energy of the arc is absorbed and consumed by this arc extinguishing fluid. Thus, the arc 15 is extinguished at the zero current point for the case of alternating current or by the current limitation for the case of direct current. Further, the current is quickly interrupted due to insulating properties of the arc extinguishing fluid.
The prior-art puffer type gas circuit breaker, constructed and operated as described above has the following disadvantages. When the current to be interrupted is great, the internal space in the nozzle 141 is occupied by the arc. A pressure rise near the nozzle attributed to the heat generated by the arc becomes greater than the pressure of the puffer chamber 11, which causes the arc extinguishing fluid from the puffer chamber 11 to be confined in the nozzle 141, and the so-called "exhaustion phenomenon" takes place in which the contact opening speed of the movable contact is reduced for positions near the full opening stroke. When the thermal energy produced by the arc is still greater, the thermal energy flows backward from the passage 14 to the puffer chamber 11 (this phenomenon is termed "arc-back") and causes the pressure to rise in the puffer chamber 11, which causes the "exhaustion phenomenon" to worsen. FIG. 2 elucidates the occurrence of the above "exhaustion phenomenon", in which dotted lines indicate characteristics in the no-load state where no current flows, and solid lines indicate characteristics in the so-called loaded state of interrupting a short-circuit current. In the figure, curves P.sub.1 and P.sub.2 denote the pressure rises of the puffer chamber, curves S.sub.1 and S.sub.2, the contact opening strokes (displacements) of the movable contact, and a curve I the short-circuit current. As seen from the figure, under the loaded state, the pressure rise of the puffer chamber becomes approximately double, and the contact opening speed becomes slower near the position of the full opening stroke. That is, the "exhaustion phenomenon" is noted. In the light of this fact, an increase in the power of an operating drive force becomes necessary for eliminating the "exhaustion phenomenon". In this manner, as the interrupting capacity of the circuit breaker is increased, the thermal energy produced by the arc increases, and the "confinement phenomenon" and "exhaustion phenomenon" described above become more noticable, so that the operating drive force requires increasingly greater power. For example, in a circuit breaker whose short-circuit current is several tens kA, the load on the operating rod in the loaded state, attributed to the "confinement phenomenon", becomes several tons (per arc extinguishing chamber) greater than that in the no-load state.